The end of They're Creeping Up on You! is perhaps the only genuinely frightening thing in the film (most everything else is deliberately silly) but it's absolutely horrifying. Also an example of Nausea Fuel and Paranoia Fuel.
Also, Richard's revenge. Being immobilized in sand while the tide gets closer and closer to you and ultimately covers you.
THAT THING, in an otherwise mostly-innocent anthology horror movie. Hint: box